Owing to variations in the cross-direction profiles, for example thickness, moisture and roughness, of the web to be wound, adjacent rolls are not formed with precisely equally large diameters, in spite of the fact that, in principle, precisely equally long component webs are wound into them. Owing to the different diameters of the rolls, the roll spools placed in the roll centers are displaced with the progress of winding in relation to one another so that their centers of rotation are separated and, at the same time, minor variations occur in the angular speeds of the rolls. Since the roll centers are, however, during the entire winding process, in contact with each other, diverting forces arise between the ends of the roll spools, and the rolls tend to "jump", in which connection the rolls that are being formed can be damaged. Owing to this detrimental oscillation, in carrier-drum winding, it is, as a rule, necessary to run at a lower speed, i.e. to be content with a lower winding speed. which reduces the capacity of the machine and is, thus, uneconomical.
The problem described above has occurred as long as winders of the carrier drum type have been in use. The seriousness of the problem has, however, varied in the course of years, because the profile of the web produced in a paper machine has improved and, at the same time, the roll size and the winding speed have changed to a little extent only. In recent years, the diameters of the customer rolls produced have started becoming ever larger and, at the same time. the winding speeds have also increased, for which reason the problem of oscillation has been noticed again: even a little variation of profile in the direction of width of the web is cumulated especially during winding of thin paper grades so that faults in the shape of the rolls which arise from the web profile cause a significant oscillation problem.
In the winding process, a number of different phenomena are effective which attempt to shift the web rolls that are being formed in their axial direction:
deflection of the winding cylinders. i.e. carrier drums, PA1 faults in the shape of the rolls arising from uneven profile of the web, and PA1 also the spool locks, which support the roll spools of the lateral web rolls, subject the row of rolls to axial forces when they keep the row of rolls in the desired location. PA1 the roll spools (web rolls) are placed one after the other coaxially so that the location of each roll spool is determined by means of the adjacent roll spools. PA1 the roll spools (web rolls) are supported under optimal conditions in the radial direction of the rolls only (the spool locks just prevent axial movement arising from faults in the roll shapes and from deflection of the winding members).
The spool locks alone can also produce a compression force applied to the whole row of roll spools when the roll spools are excessively long: the total length of the roll spools is higher than the regulated distance between the spool locks.
The phenomena described above can, either alone or together, produce situations in which the ends of the roll spools of the rolls tend to be pressed against each other and thereby to produce a relative support force.
Thus, there are several factors that produce a relative axial thrust force between the rolls. The spool locks, which keep the lateral roll spools in their positions, keep the row of rolls in the correct winding position in the lateral direction, but deflection of the carrier drums drives the rolls towards the lowest point of deflection. Variations in the web profile produce a "carrot shape" even in individual rolls, in which case the rolls tend to move in the lateral direction. Of course, variations in the lengths of the roll spools, together with the spool locks, cause variation in the axial forces in different forms. It comes out from the above that there are a number of different reasons why the rolls tend to be pressed against each other during winding.
In prior-art solutions, attempts have been made to attenuate the detrimental oscillation occurring in carrier-drum winders by various means. In the Patent DE-742,833 (granted Dec. 29, 1943), the problem of oscillation of the rolls formed by winders of the carrier-drum type has been described, and a solution has been described for reducing the oscillation. In this prior-art solution, the rolls are pressed lightly by means of a cutting roll which operates as an extra support roll, whereby attenuation of the oscillation of the rolls is produced.
A similar attenuation of oscillation produced by means of a separate roll has been applied in the Patent DE-3,924,612.
With respect to the prior art, reference is also made to the publications FI-841448 and FI-49,276, in which some typical carrier-drum winders are described, in which, of course, the detrimental oscillation problem of carrier-drum winders occurs.
It is a second prior-art mode of eliminating the problem of oscillation that relative movements of the roll spools constituting the centers of the rolls are prevented either so that an axle is placed inside the roll spools, which axle keeps the central axes of the rolls immobile in relation to one another, or so that the rolls are formed onto a continuous roll spool. In both modes, it is a drawback that separation of the rolls formed from one another causes significant additional work and, thus, also reduced productivity. Moreover, when winding takes place around the same center, the roll diameters become equally large, but, owing to variations in the cross-direction profile of the web, their internal tightness varies. This is not desirable in the procedures of further processing of the rolls.
The problems described above occur in all such winder types in which the location/support of the web rolls that are formed comply with the following terms: